<!--
title: extract repeated expressions
domain: cloud-infra
topic: Code Style
language: JavaScript
source: cloudflare/workerd
updated: 2025-08-08
url: https://awesomereviewers.com/reviewers/workerd-extract-repeated-expressions/
-->

When the same expression or computation appears multiple times within a code block, extract it to a variable to improve maintainability and readability. This reduces the risk of inconsistencies when the logic needs to be updated and makes the code's intent clearer.

Example:
```javascript
// Before - repeated computation
switch (event.event.type) {
  case 'spanOpen':
    spans.set(event.invocationId + event.spanId, { name: event.event.name });
    break;
  case 'attributes':
    let span = spans.get(event.invocationId + event.spanId);
    break;
}

// After - extract to variable
const spanKey = event.invocationId + event.spanId;
switch (event.event.type) {
  case 'spanOpen':
    spans.set(spanKey, { name: event.event.name });
    break;
  case 'attributes':
    let span = spans.get(spanKey);
    break;
}
```

This practice also applies to formatting consistency - use clear, readable formats like `10_000` instead of `10000` for large numbers to improve code readability.